Many internal combustion engines utilize fuel injectors to introduce combustible fluids into the combustion chambers of the engine. Electronic controls are generally utilized to govern operation of the fuel injectors. To allow appropriate interaction between the injector valve structure and the electronic controls, such injectors typically include a solenoid operated valve that can respond to electric signals from the electronic controls.
The electronic controls for such prior art fuel injector systems typically include a current sense unit that can provide a signal indicative of the level of current flowing through the injector solenoid. An injector drive control unit receives these signals and determines when the injector solenoid should be opened or closed. The injector drive control unit can then apply a drive signal when appropriate to an injector drive unit. The injector drive unit will selectively allow current to flow from a power source (such as a battery) through the injector solenoid and the injector drive unit.
Such prior art systems also usually include a flyback control unit. Although current flow through an inductor cannot be halted in an instant, the flyback control unit provides a means for the stored energy in the solenoid coil to be quickly dissipated and thereby assure a speedy response of the injector valve itself.
In an automotive environment, the power source usually comprises a battery. Occasionally, high voltage transients can be expected on the power bus of the automobile. Such high voltage transients can greatly disturb the proper operation of an electronically controlled fuel injection system.
To avoid the impact of such transients, many prior art systems provide transient suppressers that are intended to suppress the transient before it can get to the electronic controls or the injector solenoid. This does not represent a completely satisfactory solution, since the injector solenoid itself will often be connected directly to the battery, and the external transient suppression protection offered by the prior art may not always suffice to adequately protect the system.
On the other hand, providing additional transient protection to an electronic fuel injection control system poses other problems. Such control systems are typically small, and increasing their size to accomodate additional transient protection usually constitutes an unacceptable design alternative.
There therefore exists a need for a transient protection mechanism that will operate to adequately protect an electronically controlled fuel injection system without requiring an unacceptable redesign of the electronic controls themselves.